This invention relates to an X-ray tube unit containing within a housing an X-ray tube which includes a metal cylinder at the central portion of an envelope.
FIG. 1 shows a prior art X-ray tube unit which contains within a housing an X-ray tube with a metal cylinder at the central portion of an envelope. In this drawing, the X-ray tube 1 is screwed to projectons 7 and 8 at fixed positions on the inside wall of the housing 6 by means of supports 4 and 5 attached to an anode bar 2 and a cathode side bulb 3 of the X-ray tube, respectively. Also, a stator 9 for driving the anode of the X-ray tube is screwed to a projection 10 at a fixed position on the inside wall of the housing. The metal cylinder 11 at the central portion of the envelope is fitted with an X-ray emission window 12.
As is generally known, anode- and cathode-side ends 13 and 14 of the X-ray tube, which need be electrically insulated, are made of glass. In X-ray tubes with the central portion of the envelope formed of a metal cylinder, therefore, the metal cylinder at the central portion and the glass portions at the anode and cathode sides are joined together by a known fusion method. Thus, primary electrons from the cathode are accelerated by a high voltage to hit against a target, thereby producing quantities of secondary electrons. Part of these secondary electrons, however, will inevitably plunge into the metal cylinder of the envelope, so that electric charges will be stored gradually in the cylinder. When the charges are stored to a high degree, a potential difference is developed at the junction of the metal cylinder and the glass portions of the envelope. This potential difference brings about discharge at the junction to break the glass portions, thereby rendering the X-ray tube unusable. Moreover, the storage of the charges in the metal cylinder of the envelope will damage the uniformity of the electric field between the anode and the cathode, so that the action of the primary electron current or the X-ray tube current will lose its stability.
Such conventional X-ray tube is provided with no means for eliminating the potential difference which is produced at the junction between the metal cylinder and the glass portions of the envelope. Furthermore, the aforesaid means for attaching the X-ray tube to the housing are subject to some defects, such as too many components, extremely complex assembly, etc.